Contenu connexe Similaire à Drainage Basins (20) 1. Grade 12 Geomorphology
The Drainage Basin System
What is a drainage basin?
How does the drainage basin system operate?
Factors affecting run-off and infiltration in a drainage
basin.
Drainage Basin Management.
Stream Order.
Laminar and Turbulent flow.
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2. What is a drainage basin?
Mouth
Where the river
flows into the sea,
or sometimes a
lake.
Tributary
A river which joins a larger river.
Watershed
The boundary
dividing one
drainage basin
from another- a
ridge of high
land.
Confluence
The point at which two rivers join.
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Catchment
The area from
which water drains
into a particular
drainage basin.
Source
The upland area
where the river
begins.
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4. Drainage Basin Terminologies
Drainage Basin
An area of land drained by a river and it’s
tributaries
Watershed
The boundary between 2 drainage basins
Interfluve
High lying area between 2 stream in the same
drainage basin
Water table
Level at which saturation occurs in the soil
Groundwater
Water stored in rocks following percolation
Confluence
Where two tributaries join
Consequent
stream
Subsequent
stream
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Main stream
Main tributary
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5. Do you know your drainage basin terminology?
Click here for online
Click here for online
test
test
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6. Watershed
The drainage basin of the Afon Caerfanell, a tributary of
the River Usk, South Wales.
the watershed can
be clearly seen on
this photograph
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8. Match the label to the correct letter
Watershed
c
Confluence
Tributary
b
Source
d
a
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9. Sketch the river showing its catchment
Add the following labels – Watershed, Confluence, Tributary
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11. Learning objectives
The Drainage Basin System
What is a drainage basin?
How does the drainage basin system operate?
Factors affecting run-off and infiltration in a drainage
basin.
Drainage Basin Management.
Stream Ordering.
Laminar and Turbulent flow.
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12. All rain falling within a drainage
basin ends up in the river
system.
How does it get there?
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13. OVERGROUND
Raindrops might fall directly into a river
or stream -
Water runs downhill
over the ground towards
a river or stream SURFACE RUNOFF
CHANNEL FLOW
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15. Which route to the river is quicker
- surface runoff or infiltration / groundwater flow?
ANSWER:
Rain travelling as surface runoff
will get to rivers and streams much more quickly, reaching
a river or stream with little delay,within a short time-span.
Water that infiltrates and travels underground travels
much more slowly, finally reaching a river or stream
bit by bit over a much longer period of time.
Which situation is a river more likely to be able to cope
with, without flooding?
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16. How does the drainage basin system operate?
A drainage basin system is a part of the world’s
hydrological (water) cycle:
The hydrological cycle is a closed system.
The drainage basin is an open system.
You should be able to explain why once you have seen
the following slides!
Water Cycle
animation
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17. The water cycle – more detailed
http://www.managingwholes.co
m/flash/watercycle.htm
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19. The water cycle – definitions!
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23. Drainage basin system
inputs
stores and flows
precipitation
interception
outputs
river runoff
surface water storage
evaporation
surface runoff
transpiration
infiltration
soil water storage
throughflow
percolation
groundwater storage
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groundwater flow
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26. Learning objectives
The Drainage Basin System
What is a Drainage Basin?
How does the drainage basin system operate?
Factors affecting run-off and infiltration in a Drainage
Basin.
Laminar and Turbulent flow.
Drainage Basin Management.
Stream order.
What is a flood hydrograph?
What factors influence the shape of a flood hydrograph?
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27. Factors influencing Drainage Density
Low density (Coarse texture) are:
Factors affecting drainage density
Medium density (Medium texture)
gradient, vegetation, rock type, soil type,
evaporation, amount of rainfall, type of rainfall and
High density (Fine texture)
man.
Very high density (Superfine texture)
How do the above factors influence drainage
density?
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31. Factors affecting Drainage Density
What is:
a)Porosity
b)Permeability?
Which rock will cause the most overland flow and why?
Which rock might slow down the passage of water the
most?
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33. A number of factors will effect how quickly water gets
to a river.
If water returns to a river too quickly it may result in
flooding.
Look at the following slides (35-39)
How do you think they affect how quickly water
returns to the river?
Explain how each of these factors will affect drainage
density. Insert you answer in a textbox.
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39. Flood Controls
•
Reduce run-off in the upper areas of the
river by ensuring that the slopes are
covered with vegetation.
Use terraces and contour ploughing in
farmlands to help control surface runoff.
Build dams to control the flow of water
through an area.
Don’t build
settlements in areas
below the floodline.
Flooding in Australia
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Build levees that can withstand the
pressure and high water levels.
Build larger channels and divert water
away from certain areas.
Powerpoint
Coastal flooding
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40. Activity 4: Causes and impacts of floods
Pg.119
(5)
(3)
(3)
(5)
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43. Learning objectives
What is a drainage basin?
How does the drainage basin system operate?
Factors affecting run-off and infiltration in a drainage
basin.
Drainage Basin Management.
Stream Order.
Laminar and Turbulent flow.
What is a flood hydrograph?
What factors influence the shape of a flood hydrograph?
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45. Learning objectives
What is a Drainage Basin?
How does the drainage basin system operate?
Factors affecting run-off and infiltration in a Drainage
Basin.
Drainage Basin Management.
Stream Order.
Laminar and Turbulent flow.
What is a flood hydrograph?
What factors influence the shape of a flood hydrograph?
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46. Stream order
• A method of classifying or ordering the
hierarchy of natural channels.
• Strahler (1957) is the most widely used
system.
• See GIS stream
ordering
www.usda.gov/stream_restoration/chap1.html
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47. Law of Stream Numbers and Law of Basin areas.
The law a stream numbers states that the higher the a drainage basin increases from one
There is of fairly fixed regularity with which the area of stream order the fewer the number of
tributaries e.g. the will this is be more the law of basin areas. The in a regularity is 4,7
stream order totherenext alwaysknown as stream order ones than [two’s fixedgiven drainage
basin.
times]
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48. Calculation of area according to the squares method
Count the number of WHOLE squares
that fall within the outline
1 cm
1cm
Number of squares fully
covered = 18
Count the number of squares covered
by + half
Number of squares covered
by +half = 7
Total number of square covered =25
Area of one square = LXB
= 1cm x 1cm
= ,5 km X ,5 Km = ,25 square Km
Area of 25 squares
= ,25 X ,25 = 6,25 square Km
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49. Calculation of Drainage Density
Stream order at X = 4
1 cm
1 cm
Number of squares
fully covered = 42
Number of squares cove
by more
than half = 13
Total number of
Squares = 55
Area of 1 square
=LXB
= 1cm X 1cm
= ,5 km X ,5 km
= ,25 square km
Area of 55 squares
= 55 x ,25 sq. km
= 14 sq. km
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50. Learning objectives
What is a drainage basin?
How does the drainage basin system operate?
Factors affecting run-off and infiltration in a drainage
basin.
Drainage Basin Management.
Stream Ordering.
Laminar and Turbulent Flow.
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51. Laminar Flow
River-bed is level and even
Turbulent Flow
Water flows in layers
Water in contact with the bed and banks flows slowly due
to friction
Successive layers achieve greater speeds. Fastest
speeds occur in the middle just below the surface
Water travels faster, but there is less erosion since
the lower layers protect the river channel.
River-bed is uneven and steep
Water continually changes levels and flows with a
‘bubbling’ action
Lots of erosion takes place, because the sand
particles are lifted by water.
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53. What do you know about drainage basins?
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Notes de l'éditeur The section on Groundwater in the textbook is out of the syllabus – direct, indirect drainage, acquifers (Gravel, sandstone, conglomerate), acquicludes (clay, shale, Granite), springs and artesian wells. Meteoric water (ground water) Magmatic water, Connate water (found is Sed rocks)
Pg 111, 112 and 113.
Gradient more runoff and less infiltration if there is a steep slope. Less runoff therefore the drainage density will be lower.
Low drainage density 1km of river flowing in 1 km sq drainage basin.
Extremely high drainage density (eg. Badlands) 700 km of river flowing in 1 km sq drainage basin
Stream order helps to conceptually organize the streams in a watershed.
As streams increase in order, they also increase in length, exponentially;
World-wide, about 70-75% of stream miles occur as headwater (first order) streams.
